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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        class strong {
            constructor(x, y) {
                this.x = x
                this.y = y
            }
            supmang() {
                console.log(this.x + this.y);
            }
        }
        var down = new strong(8, 4)
        down.supmang()
        class Son extends strong {
            constructor(x, y) {
                super(x, y)
                this.x = x
                this.y = y
            }
            sumber() {
                console.log(this.x * this.y);
            }
        }
        var downs = new Son(8, 6)
        downs.supmang();
        downs.sumber();
    </script>
</body>

</html>